Car Heater Repair & Troubleshooting

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Use caution when working around radiator & heater, hoses and coolant. They can be very hot. Never open the radiator cap when the engine is hot, antifreeze / water can spray out. Use of safety goggles is suggested.

TIP: With a rag or glove to protect your hands from being burned, gently squeeze radiator hose to check for pressure before opening the radiator cap.

A few tips troubleshooting your car heater.

The most common problem is low engine coolant level and/or low engine temperature. Temperature from the heater outlets should be 130 degrees or more with the fan on high after the car has warmed up.

In cars five years old or newer is the most common problem is a faulty engine thermostat.

The older the vehicle, the more likely problems are the heater core and / or multiple other problems.

A heater core works like the car radiator. Coolant from the engine circulates through the core, air blows through the core and into the passenger compartment. Heater cores can become plugged, and may require flushing or replacement. Two hoses go from the the engine to the heater core, and can develop pin-hole leaks that only show up under pressure, as when the engine is hot. Flush kits are available from auto parts stores to use a garden hose to flush the heater core and radiator.

Tracking it down:
If your vehicle has a temperature gauge, check it to see if it is in the normal range. To check the temperature yourself, you can use a metal case candy thermometer placed into the filler on the radiator when the engine is COLD. Start the car and let it warm up, the temperature in the radiator should be around 180 degrees on older cars, up to around 205 on newer ones. Be careful, the engine may start to boil over if you leave it running too long with the cap off.. Keep face and hands away from opening, and wear protection for eyes and hands..

If the engine temperature and fluid level are correct, the next most common problem is poor circulation through the heater core. With the motor running and at full operating temperature, CAREFULLY feel the heater hoses. (Use of a rag may help protect hands) Both hoses should be similar in temperature. If one hose is considerably cooler then the heater is restricted. Flushing the heater works sometimes but replacement is often necessary.

Depending on the vehicle, the temperature control lever may control a water valve in series with the heater core, or an air door that mixes hot and cold air. The lever may operate via wire cable or vacuum controls. There can be problems in the control valve, cable, vacuum line, or vacuum diaphragm ( sometimes called a vacuum motor ) that controls air doors.

Water pumps can have insufficient flow. Restriction in heater hose connections at the intake or water pump will slow the flow through the heater. The antifreeze - water mixture can effect heat transfer. A 50% / 50% mix will transfer more heat and also has a lower freezing point than 100% antifreeze, ( check your owner's manual for the recommended mix - the freezing point actually starts to rise above about a 70% mix)

Remember for good heat you need hot water and air flow so start with the basics and you'll most likely find the problem. Heater cores on some cars can be difficult to replace, taking your vehicle to a good radiator repair shop may be in order.

These tips courtesy of .

Indianapolis Radiator Works
New - Custom - Automotive - Truck - Industrial Radiators
Repairing, Recoring, Industrial, Commercial radiators.
Wholesale & Retail
Shipping available.
108 S. Rural St.
Indianapolis, IN 46201
317-634-6315
1-800-RAD0540